Any good DIY amps for low impedence/high sensitivity headphones? - Page 2 - diyAudio
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Old 21st June 2012, 11:49 AM   #11
Telstar is offline Telstar  Italy
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Originally Posted by ethanolson View Post
I'm with @jcx on this one. I recommend you go after a CMOY with unity gain (i.e. a buffer), but configured with <1Z to get all the benefit possible from your 'phones.
I really DONT think jcx was thinking to the cmoy, nor any other IC-based output stage cause they dont have the required current to drive low Z 'phones.
"The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
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Old 21st June 2012, 01:54 PM   #12
jcx is offline jcx  United States
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some single op amps have plenty of current, but may not like the load Z

adding series R is OK for flat impedance curve headphones, can make a R divider "L-pad" but then need excess current capacity to "waste" in order to get lower drive Z to the headphone (== deliberate Z mismatching)

at the extreme it depends on what you consider low z, high sensitivity

JH Audio JH16 IEM:
118dB @ 1mW
Impedance: 18 Ohms

~200 mV, 10 mA peak to get to ~120 dB SPL

clearly the only rational way to drive these from 1-2 Vrms standard audio sources involves a step down transformer

Last edited by jcx; 21st June 2012 at 01:58 PM.
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Old 21st June 2012, 02:54 PM   #13
haejuk is offline haejuk  United States
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I have pretty much decided to build a 2 channel Beta22 with low gain. I may get other headphones in the future and have to change the gain settings, but a Beta22 should drive anything I throw at it admirably.

I had looked into making something that is just a current source + attenuator, but there don't seem to be any viable (well documented) designs.

In fact, I think it was a post on another forum by jcx that convinced me to go 2 channel on my Beta22 build instead of 3 channel.

Last edited by haejuk; 21st June 2012 at 02:59 PM.
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Old 21st June 2012, 03:12 PM   #14
jcx is offline jcx  United States
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TPA6120 is designed for 25 Ohm load, good audio specs by itself - some headphone project amps use it

some may not know but CFA op amps can be used "unity gain" - you still need a feedback R between the output and -in
its value provides frequency response compensation, increasing it provides "overcompensation" - less peaking, better immunity to destabilizing C load

better (but probably inaudible) performance can be had by wrapping a "good", "audio" input op amp feedback loop around a CFA buffer op amp in a multiloop composite amplifier
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Old 21st June 2012, 04:28 PM   #15
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I've been liking the use of the NJM4556D that the Objective2 employs. That thing can handle 1 Ohm to 600 Ohm and puts out about 70mA... enough for every headphone out there (other than the K1000) to get over 105dB.

Anyway, I was thinking you would've liked to build something like this:

I hope the Beta22 turns out nicely.

Last edited by ethanolson; 21st June 2012 at 04:34 PM. Reason: I'm smarter now than I was before.
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Old 21st June 2012, 06:17 PM   #16
haejuk is offline haejuk  United States
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I did actually build an Objective2, and I think that it simply can't be beat for the price of parts, or its retail price for that matter. I had considered building another one and putting it in a larger enclosure for desktop use, but decided to try a Beta22. I might take a crack at some of the other amps mentioned in this thread as well, since I find building these things just as much fun as listening to them.
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Old 22nd June 2012, 02:38 PM   #17
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Other than the B22, AMB has a few other offerings such as the CKKIII, M3, or even the A20 that can be configured as unity gain buffer. Or you can make a simple tube voltage gain stage to drive the A20 buffer if you fancy a hybrid.

I have only build the B22 but all of them are supposed to be good. Glass jar audio offer kits for some of these and all you have to do is put them together.

They also have other kits such as the SOHA II, EHHA and the Bijou from Cavalli audio. FWIW I prefer the SOHA II over the B22.
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